Sheet feeding assemblies engage and remove sheets of paper or other media from a stack and feed the sheets along a path to a printing zone, copying zone, scanning zone or the like.
During operation, a sheet picker, usually a small roller having a high friction rubber circumference, engages and removes the uppermost sheet from a stack and feeds it edgewise along a feed path through to a sheet separator.
The sheet separator ensures that only one sheet is fed along the sheet path and separates any multiple sheets. A common type of sheet separator includes an advancing roller aligned adjacently and pinched with a reversing roller, both rollers have a high friction gripping surface. The advancing roller is driven in a sheet advancing direction while the reversing roller is driven to move a sheet in a reverse direction. The advancing roller provides a stronger positive force between the two rollers such that when they are pinched with a single sheet therebetween, the advancing roller causes the reversing roller to change direction and move in unison to move the sheet forward. The reversing roller is coupled to a torque limiter, which allows the reversing roller to slip with respect to the drive and hence to counter-rotate.
Where more than one sheet is picked and passes through to the sheet separator, the advancing roller engages with the top-most sheet while the reversing roller engages with the bottom-most sheet. The lack of resistance between the sheets means that the advancing roller cannot impart any frictional force to the reversing roller and hence the reversing roller is allowed to rotate in a reversing direction moving the bottom most sheet backwards while the top-most sheet is moved forward.
The feeding assembly must be able to quickly and efficiently feed each individual sheet in the queue to the printing, copying or scanning zone without creating a backlog and without jamming. This is particularly important where the sheets to be fed are original documents to be copied or scanned and cannot risk being damaged.
Generally, these sheet separators work well but are limited in the speed at which they can advance paper. This limitation is based on the limitations of the torque limiter, which will only allow the reversing roller to counter-rotate up to a certain speed dictated by the torque limiter's working mechanism.
It is therefore desirable to produce a sheet separator that can effectively function at high feeding speeds.